P1- Energy for the Home Flashcards
What happens when the energy flows away from a warm object?
The temperature decreases
Which colours show what temperature in a thermogram?
- white/ yellow - hot
- black/ dark blue/ purple - cold
What happens to the **kinetic energy **when the temperature of a body increases?
The average kinetic energy of the particles increases
What is heat and temperature a measurement of?
And what scale is used?
- heat is a measurement of internal energy and measured on the absolute scale
- temperature is a measurement of hotness on an arbitrary scale
What is specific heat capacity?
Energy needed to raise the temperature of 1kg by 1°C, measured in **joules per kilogram degree Celsius **(J/kg °C)
How do you calculate energy transfer by specific heat capacity?
energy transferred =
mass x specific heat capacity x temperature change
What is specific latent heat?
The energy needed to melt or boil 1kg of the material, measured in **joule per kilogram **(J/kg)
How do you calculate energy transfer by specific latent heat?
energy transferred = mass x specific latent heat
How does double glazing reduce energy loss by conduction?
The gap between the two pieces of glass is filled with a gas or contains a vacuum
Why does the vacuum reduce energy transfer?
Because there are no particles, so it is impossible to transfer energy by conduction
How does loft insulation** **reduce energy loss by conduction?
- warm air in home rises
- energy is transferred through the ceiling by conduction
- air in loft is warmed by the top of ceiling and trapped in loft insulation
- no energy is transferred as both sides of the ceiling are the same temperature
How does loft insulation reduce energy loss by convection?
- without loft insulation, the warm air in the loft can move by convection and heat the roof tiles
- energy is transferred to the outside by conduction
How does cavity wall insulation reduce energy loss?
- air in the foam is a good insulator
- air cannot move by convection because it is trapped in the foam
How do insulation blocks reduce energy transfer by radiation?
Covered in shiny foil so:
- energy from Sun is reflected back to keep homes cool in summer
- energy from home is reflected back to keep homes warm in winter
How can energy be transferred by conduction?
Due to the transfer of kinetic energy between particles
How can energy be transferred by convection?
A gas expands when heated, making it less dense so it rises.
How can you measure density?
**density (kg/m3or g/cm3) **= mass/ volume
How can energy be transferred through a vacuum?
Radiation does not need material to transfer energy, so can be transferred.
How can you calculate energy efficiency?
**efficiency = useful energy output / total energy input **(x 100%)
How can energy transformations be shown?
Through Sankey diagrams
How can you calculate payback time?
payback time = cost of insulation / annual saving
What is the **amplitude **of a wave?
The maximum displacement of a particle from its rest position
What is the crest / peak and trough of a wave?
- crest - highest point on a wave above its rest position
- trough- lowest point on a wave below its rest position
What is the frequency of a wave?
The number of complete waves passing a point in one second
How can you calculate wave speed?
wave speed = frequency x wavelength
Name the parts of the Electromagnetic Spectrum
- radio
- microwave
- infrared
- visible
- ultraviolet
- X-ray
- gamma ray
How does **refraction **work?
The speed of the waves decrease as the wave enters a more dense medium and increases as the wave enters a less dense medium. The frequency stays the same but wavelength changes
What is diffraction?
The spreading out of a wave as it passes through a gap
How does diffraction change?
Most diffraction occurs when the gap is a similar size to the wavelength. Larger gaps show less diffraction
What is the Morse code?
A series of dots and dashes to represent letters of the alphabet
What type of signal is the Morse code?
Digital
What is the Morse code used for?
Signalling lamps as a series of short and long flashes of light
What is white light made of?
Different colours of different frequencies out of phase
What is laser light made of?
Single frequency, in phase and shows low divergence
How is laser light used for a Compact Disk (CD)?
- surface of CD is pitted
- pits represent the digital signal
- laser light is shone onto the CD surface and difference in reflection provides the information for the digital signal
What is refraction?
When light passes from two materials of different densities and changes direction
What happens to the angles when light passes from a more dense material to a less dense material?
The angle of refraction is larger than the angle of incidence
What is the critical angle?
When the angle of refraction is 90°
What is total internal reflection?
When the angle of incidence is bigger than the critical angle, the light is reflected
How is TIR used for optical fibres?
Telephone conversations and computer data are transmitted long distances at the speed of light
How does an **endoscope **work?
- light passes along one set of optical fibres to illuminate the inside of the body
- light is reflected
- reflected light passes up another set of fibres to an eyepiece or camera
How well doe **infrared **penetrate food?
Not very easily
How far does **microwave **radiation penetrate food?
1 cm into food
What materials can penetrate or reflect microwaves?
- penetrate glass or plastic
- reflect shiny metal surfaces
Why does a microwave have a glass door?
- reflects the microwaves
- so it does not burn body tissue
What does the amount of energy depend on?
Frequency or wavelength of wave
What frequency/ wavelength transfer more energy?
- High frequency
- Short wavelength
How do ovens cook food by infrared radiation and microwave ovens by microwave radiation?
- energy absorbed by surface of food
- kinetic energy of surface food particles increases
- rest of food is heated by conduction
- water or fat molecules in outer layers of food vibrate more
What wavelength range do microwaes have?
Between 1 mm to 30 cm
What wavelength is used by mobile phones and how much energy is transferred?
- longer wavelengths than microwave ovens
- less energy is transferred by mobile phones
What is microwave radiation used for?
Communicating over long distances
What must **transmitters **and **receivers **be with each other?
In line of sight
Where must aerials be situated?
On top of high buildings
What are satellites used for?
Microwave communication
How do satellites work?
- signal from Earth is received, amplified and re-transmitted back to Earth
- in line of sight because there are no obstructions in space
What are the concerns of use of mobile phone and positioning of phone masts?
- exposure to radio waves
- can cause cancer if too much exposure
How can signals be affected?
- adverse weather and large areas of water can scatter signals
- curvature of the Earth limits line of sight, so transmitters have to be on tall buildings
- microwaves do not show much diffraction
What do infrared signals carry?
Information that allows electronic and electrical devices to be controlled
What does a digital signal look like?
What does an analogue signal look like?
What does the switchover from analogue to digital do for TV and radio?
- improve signal quality for both picture and sound
- a greater choice of programmes
- being able to interact with the programme
- information services such as programme guides and subtitles
What do optical fibres allow?
Data to be transmitted very quickly using pulses of light
Before an analogue signal is transmitted, where is it added to?
A carrier wave
What is the frequency of the carrier wave?
Higher than the signal being transmitted
What is multiplexing?
Combination of multiple signals into one signal trasmitted over a shared medium
What is wireless technology used by?
- radio and television
- laptops
- mobile phones
What happens to radio waves in the Earth’s atmosphere?
It is reflected and refracted:
- amount of refraction depends on the frequency of wave
- there is less refraction at higher frequencies
Why can same frequencies be used by more than one radio station?
- radio stations are too far away from each other to interfere
- in unusual weather, radio waves can travel further and the broadcasts interfere
How can interference be reduced?
By using digital signals
What does Digital Audio Broadcasting (DAB) provide?
- greater choice of radio stations
- audio quality is not as good as FM signals
- eliminates interference between other radio stations
How are radio waves affected by the ionosphere?
They are reflected:
- behave like light in an optical fibre
- undergo total internal reflection
What does and does not reflect radio waves?
Water reflects but land does not
How are microwaves affected by the ionosphere?
They pass though it
Where do communication satellites orbit?
Above the equato and take 24 hourse to orbit Earth
What are communication problems?
- radio waves are diffracted when they meet an obstruction
- refraction in atmosphere needs to be taken into account
- transmitting aerial needs to send a focused beam because its aerial is very small
- trasmitted beam is slightly divergent
- energy is lost from the edge of transmitting aerial because of diffraction
What does a seismograph show?
Different types of earthquake waves
What are P waves?
- longitudinal pressure waves
- travel through Earth at 5km/s - 8km/s
- can pass through solids and liquids
What are S waves?
- transverse waves
- travel through Earth at 3km/s - 5.5km/s
- can only pass through solids
How are P waves affected by the core?
- refracted by the core
- paths taken by P waves allow scientists to work out the size of the core
How are S waves affected by the core?
- not travel through liquid
- allows scientists to determine that the core is liquid
What does ultraviolet light cause?
A tan on skin
What cell produces a tan?
Melanin produces a pigment that causes a tan
Why do darker people not tan as easily?
The UV radiation is filtered out
How do you calculate the time to spend in Sun?
maximum length of time to spend in the Sun = published normal burn time x SPF
Where is ozone found?
In the stratosphere
What does ozone do?
Filter out UV radiation
What was the main cause of reducing the ozone layer?
Gases from aerosols and firdges
Where is the ozone thinnest?
Above the South Pole because ozone depleting chemicals work best in cold conditions
